Electrically driven type injection molding apparatus

ABSTRACT

An injection molding apparatus uses motors to effect measuring and kneading of a material to be molded and injection driving. The amount of movement of a rotary shaft or rectilinearly moving means connected to a screw is detected by a sensor, and the driving of the volume measuring motor and the injection motor is effected by the output of the sensor.

This application is a division of U.S. patent application Ser. No.07/514,751 filed Apr. 26, 1990 now U.S. Pat. No. 5,110,522.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to an electrically driven type injectionapparatus, and more particularly to an electrically driven typeinjection apparatus in which the rotational movement and rectilinearmovement of a screw for kneading and injecting a material to be moldedare effected by an electric motor.

2. Related Background Art

In an injection molding method wherein a material to be molded such asplastic is injected into a molding metal mold to thereby manufacture amolded article, use has heretofore been made chiefly of hydraulic typeand electrically driven type injection apparatuses.

Here, a hydraulic type injection apparatus according to the prior artwill first be described with reference to FIG. 9 of the accompanyingdrawings.

This hydraulic type injection apparatus is comprised chiefly of a hopper71, a screw 73 for mulling and measuring resin amount charged from thehopper in a cylinder 72, a motor 51 for rotatively driving the screw,and a direct-acting type cylinder 52 for injecting the kneaded resin,and the motor 51 and the direct-acting type cylinder 52 have usuallyadopted the hydraulic driving type in which a great output can be easilyobtained.

An electrically driven type injection apparatus disclosed in JapanesePatent Publication No. 61-57168 will now be described with reference toFIG. 10 of the accompanying drawings.

In FIG. 10, the reference numeral 53 designates a screw contained in aheating cylinder 66. This screw is fixed to a driven gear 54 forrotating the screw which is disposed rearwardly. The reference numeral56 denotes a support member slidably guided by a guide bar 57. Thissupport member rotatably supports the driven gear 54 for rotating thescrew and has secured thereto a ball nut 55 to which is fitted a ballbearing screw 58 whose fore end bears against the shaft of the gear 54.A driven gear 59 for propulsion is secured to the ball bearing screw 58.The driven gear 54 for rotating the screw and the driven gear 59 forpropulsion are disposed above the rotary shaft of a motor 62, and areconnected to driving gears 63 and 64, respectively, which are connectedtogether by clutches 60 and 61.

In this apparatus, there is also provided a back pressure brake unit 65behind the driven gear 59 for propulsion so that the retractingoperation of the screw 53 may be effected from rearward of this gear 59.Thus, when the screw 53 is retracted by the kneading and measurement ofresin charged from a hopper 74 into a heating cylinder 66, the ball nut55 retracts through the gear 54 and the support member 56, and the ballbearing screw 58 is rotated and in accordance therewith, the gear 59 isrotated. When the end surface of this gear 59 which is being rotated ispressed by the back pressure brake unit 65, the rotation of the gear 59can be braked by a slip torque created between the two and thus, theback pressure against the screw 53 may be provided.

However, the above-described injection apparatuses according to theprior art have suffered from problems as mentioned below.

In the hydraulic type injection apparatus as shown in FIG. 9,

(1) a hydraulic pump and surrounding devices such as piping facilitiesare required and therefore, a wide installation space for the injectionmolding apparatus is required, and

(2) because of oil mist or the like produced from a hydraulic drivinginstrument, it is impossible to use the injection molding apparatusunder a clean environment.

On the other hand, in the electrically driven type injection apparatusas shown in FIG. 10, the problems peculiar to the hydraulic typeinjection apparatus are eliminated, but

(1) to impart back pressure, it is necessary to control this backpressure by the sum of a force for converting the rectilinear movementof the ball nut, etc. during the retraction of the screw into therotational movement of the ball bearing screw, etc. and a force producedfrom slip torque by a brake pressed against the end surface of a gear orthe like and therefore, there are required many parameters for the backpressure (such as the rotational resistance of the ball bearing screw orthe like, the frictional force of a brake plate and the produced outputof the brake) and the setting of conditions becomes complicated, and

(2) because of a construction in which the rotatively driven gear andthe propulsion-driven ball nut are supported by one and the same supportmember and are moved with the screw at a time, a guide for stopping therotation of the support member becomes necessary and a wide installationspace around the driving system is required, and the constructionbecomes complicated.

SUMMARY OF THE INVENTION

It is a first object of the present invention to provide, in aninjection molding apparatus wherein the kneading, measurement andinjection operation of a material to be molded are controlled by motors,a molding method capable of accurately accomplishing the control of themeasurement and kneading and the control of injection molding.

More particularly, the present invention proposes a molding method inwhich rectilinearly moving means for converting the rotation of saidinjection motor into rectilinear movement is connected to said screwthrough a rotary shaft, said screw and the volume measuring motor areconnected together through said rotary shaft, and the control of saidvolume measuring motor and the control of said injection motor areeffected by the detection of the amount of movement of saidrectilinearly moving means and/or said rotary shaft, whereby the drivingof each motor is accurately effected to thereby obtain a highly accuratemolded article.

Further, in the present invention, said volume measuring motor and saidinjection motor cause the movement of said rectilinearly moving meansand said rotary shaft to be detected by a sensor and the output signalof this sensor is logically controlled to thereby effect the driving ofeach motor.

It is another object of the present invention to provide an electricallydriven type injection apparatus in which a device for imparting the backpressure of a screw and a control source therefor are constructed of asimple mechanism and the compactness of screw propulsion and rotationmechanisms is made possible.

In order to solve the task as noted above, the electrically driven typeinjection apparatus of the present invention is characterized by a screwfor kneading a material to be molded in a cylinder and injecting thematerial therefrom, a first motor for rotating said screw and measuringthe amount of the material, a back pressure cylinder connected to therear of said screw for imparting back pressure to said screw,rectilinearly moving means connected to the rear of said back pressurecylinder for rectilinearly moving said back pressure cylinder, and asecond motor for driving said rectilinearly moving means.

It is still another object of the present invention to provide aninjection apparatus which is made compact by constructing the injectionapparatus which has heretofore been constructed of a complicatedmechanism by a simple mechanism.

In order to solve the above-noted task, the electrically driven typeinjection apparatus of the present invention is an electrically driventype injection apparatus in which the rotational movement andrectilinear movement of a screw contained in a heating cylinder areeffected by an electric motor, characterized in that a rectilinearymoving mechanism and a rotating mechanism for said screw and a backpressure mechanism are disposed in series on the propulsion shaft ofsaid screw.

In the aforedescribed prior-art apparatuses shown in FIGS. 9 and 10, toimpart back pressure, it is necessary to control this back pressure bythe sum of a force for converting the rectilinear movement of the ballnut or the like during the retraction of the screw into the rotationalmovement of the ball bearing screw or the like and a force produced fromslip torque by the brake pressed against the end surface of the gear orthe like and therefore, there are required many parameters for the backpressure (such as the rotational resistance of the ball bearing screw orthe like, the frictional force of the brake plate and the producedoutput of the brake) and the setting of conditions becomes complicated.The back pressure regulating method of the present invention comprisesconnecting an injection motor to a screw for injecting a material to bemolded kneaded in a heating cylinder through a rectilinearly movingmechanism for converting the rotational movement of the motor intorectilinear movement, and causing a load for back pressure regulation toact on said rectilinearly moving mechanism by the rotational movement ofsaid injection motor with the retraction of said rectilinearly movingmechanism being permitted during weight measurement.

Further, the present invention proposes, in an injection moldingapparatus wherein the injection operation is effected by a volumemeasuring and kneading motor and an injection motor, a novelconstruction of a mechanism for converting the rotation of the motorsinto rectilinear movement. That is, in the motor type injectionapparatus according to the present invention, a ball nut receivingmember is fixed to a rotary shaft having connected thereto a screw forinjecting a formed material, a ball bearing screw connected to theoutput shaft of an injection motor is threadably engaged with a ball nutsecured to the ball nut receiving member, a volume measuring motor isconnected to said rotary shaft through a rotation transmitting gear, andsaid volume measuring motor is braked during the rotative driving ofsaid injection motor, whereby the rotation of said ball nut may bestopped.

The electrically driven type injection apparatus of the presentinvention is an electrically driven type injection apparatus in whichthe rotational movement and rectilinear movement of a screw contained ina heating cylinder are effected by an electric. The injection apparatusfeatures a rotating mechanism, a rectilinearly moving mechanism and aback pressure mechanism disposed on the rear of said screw coaxiallywith said screw in the order of the rotating mechanism, therectilinearly moving mechanism and the back pressure mechanism or in theorder of the rectilinearly moving mechanism, the rotating mechanism andthe back pressure mechanism. The rotating mechanism has a rotary shaftwhich rotates said screw, on which said screw is axially movablyprovided, and a first rotative driving force transmitting mechanism fortransmitting the rotative driving force from said motor to said rotaryshaft. The rectilinearly moving mechanism has a guide shaft havingrestraining portions on the opposite ends thereof, a hollow ball bearingscrew slidably fitted to said guide shaft and provided so as to berestrained by each restraining portion, a ball nut threadably engagedwith said hollow ball bearing screw, and a second rotative driving forcetransmitting mechanism for transmitting the rotative driving force fromsaid motor to said ball nut. In addition, the back pressure mechanismhas a back pressure cylinder, and a cylinder rod for pressing said guideshaft or said rotary shaft.

As described above, the electrically driven type injection apparatus ofthe present invention comprises, as main elements, a screw contained ina cylinder, a rotating mechanism for rotating this screw, a forwardlymoving mechanism for forwardly moving the screw, and a back pressuremechanism for imparting back pressure to the screw. The rotatingmechanism and said forwardly moving mechanism are disposed coaxiallywith said screw in the order of the rotating mechanism and the forwardlymoving mechanism or in the order of the forwardly moving mechanism andthe rotating mechanism. The back pressure mechanism for imparting backpressure to the screw is provided on the rear of said rotating mechanismor said forwardly moving mechanism of the above-described construction.Accordingly, these elements are of a construction in which they aresuccessively arranged on the propulsion shaft of the screw, and forexample, by disposing each element vertically, the installation area forthe entire apparatus may be very small.

As regards the rotating mechanism for the screw, an electric motor and arotary shaft for rotating this screw are connected together by the firstrotative driving force transmitting mechanism, whereby the rotativedriving force of the motor can be transmitted to the screw.

The forwardly moving mechanism for the screw comprises a ball bearingscrew mechanism and said electric motor connected by the second rotativedriving force transmitting mechanism to the ball nut of the ball bearingmechanism which comprises a guide shaft having restraining portions onthe opposite ends thereof, a hollow ball bearing screw slidably fittedto the guide shaft and provided so as to be restrained by eachrestraining portion, and a ball nut threadably engaged with the hollowball bearing screw, whereby when the ball nut is rotated, the hollowball bearing screw slides on the guide shaft to thereby push out therestraining portions of the guide shaft, whereby propulsion can beimparted to the screw.

In the injection apparatus of such construction, a clutch mechanism canbe provided for the first and second rotative driving force transmittingmechanisms, and by the change-over of this clutch, the drive source ofeach rotative driving force transmitting mechanism can be constructed ofa single electric motor.

The back pressure mechanism for the screw has a back pressure cylinderand a cylinder rod provided therein, and by this cylinder rod acting onsaid rotating mechanism or said forwardly moving mechanism, backpressure can be imparted to the screw. This back pressure mechanism isof the cylinder-driven type and therefore is simple in construction, anda control source therefor can also be constructed of a simple mechanism.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view of an electrically driventype injection apparatus according to an embodiment of the presentinvention.

FIG. 2 is a perspective view of the vicinity of a rotating mechanism, arectilinearly moving mechanism and a back pressure mechanism in FIG. 1.

FIGS. 3A-3E illustrate the operation of the electrically driven typeinjection apparatus shown in FIG. 1.

FIG. 4A comprised of FIGS. 4A-1 and 4A-2 is a flow chart of theinjection molding by the electrically driven type injection apparatusshown in FIG. 1.

FIG. 4B is a block diagram.

FIG. 5A illustrates the concept of an electrically driven type injectionapparatus according to a second embodiment of the present invention.

FIG. 5B is a cross-sectional view taken along line II--II in FIG. 5A.

FIG. 5C is a cross-sectional view taken along line III--III in FIG. 5A.

FIG. 6 is a perspective view of the vicinity of a rotating mechanism, arectilinearly moving mechanism, a back pressure mechanism, a clutch andan electric motor in FIG. 5.

FIGS. 7A-7E and 8A-8B are an illustration and a flow chart,respectively, of the operation of the second embodiment.

FIG. 9 is a cross-sectional view of a hydraulic type injection apparatusaccording to the prior art.

FIG. 10 is a cross-sectional view of an electrically driven typeinjection apparatus according to the prior art.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

An embodiment of the present invention will hereinafter be describedwith reference to the drawings.

FIG. 1 is a schematic cross-sectional view of an electrically driventype injection apparatus according to the present embodiment, FIG. 2 isa perspective view of the vicinity of a rotating mechanism, arectilinearly moving mechanism and a back pressure mechanism, FIGS.3A-3E illustrate the operation of the present embodiment, and FIG. 4 isa flow chart of the injection molding by the apparatus of the presentembodiment.

In the electrically driven type injection apparatus of the presentembodiment, as shown in FIGS. 1 and 2, a screw 2 contained in a heatingcylinder 1, a rotary shaft 3 fixed to the rear of the screw 2 by a pin4, a follower side spur gear 6 secured by a key 5 to an intermediaterotary shaft 3a comprising the upper portion of the rotary shaft 3 whichis reduced in diameter from the lower portion of the rotary shaft, aback pressure cylinder 12 designed to push out the rotary shaft 3, arecti-linearly moving cylinder 13 integrally connected to the upperportion of the back pressure cylinder through a partition wall 14, andan injection motor 23 provided through a coupling 25 on a ball bearingscrew 24 fitted to a ball nut 22 secured to the rear of therectilinearly moving cylinder are disposed longitudinally on the samestraight line as the screw 2.

The reference numeral 32 designates a hopper. A material to be moldedcharged into this hopper is supplied into the cylinder 1 through a pipe31.

A through-hole 34 is formed in the central portion of the shoulder 19 ofthe rectilinearly moving cylinder which is formed on the lower endportion of the back pressure cylinder 12, the intermediate rotary shaft3a of the rotary shaft 3 is slidably provided in the through-hole 34,and further an upper rotary shaft 3b of smaller diameter than theintermediate rotary shaft 3a is rotatably provided on the upper portionof the intermediate rotary shaft 3a through a bearing unit 11 providedin the hollow portion of a piston 10. However, the upper rotary shaft 3bis engaged with the bearing unit 11 at the upper end portion of theupper rotary shaft 3b so as to follow the vertical movement of thepiston 10. A packing 15 is fitted to the outer periphery of the pistonin the back pressure cylinder 12, and further a lid portion 16 is fittedto the central upper portion of the piston to thereby prevent theleakage of compressed fluid supplied into the back pressure cylinder.

Sideways of the rotary shaft 3, a volume measuring electric motor 7 forrotatively driving a drive side spur gear 8 meshing with the followerside spur gear 6 secured to the intermediate rotary shaft 3a is mountedon an injection unit base 33. The drive side spur gear 8 has a widetooth form and will never be disengaged from the follower side spur gear6 even if the rotary shaft 3 moves up and down.

By such a construction, the volume measuring motor 7 rotatively drivesthe rotary shaft 3 to thereby rotate the screw 2 in the cylinder 1, andeffects measurement while kneading the material to be molded in thecylinder. The volume measuring motor 7 and the injection motor 23 areconnected to a controller 30, whereby the respective motors can becontrolled.

A protruded piece 20 having its tip end bifurcated is provided sidewaysof the rectilinearly moving cylinder 13, and a through-hole formed inthis protruded piece is slidably fitted over a guide shaft 21 secured tothe injection unit base 33. The guide shaft 21 is provided in parallelwith to the screw 2, and by the rectilinearly moving cylinder 13 beingguided and moved by the guide shaft 21, the rectilinearly movingcylinder 13 can be moved vertically only in the direction of propulsionof the screw 2.

The rectilinearly moving cylinder 13 can be moved vertically by the ballbearing screw 24 being rotated by the guiding action of the guide shaft21 and the rotative driving of the injection motor 23 and the ball nut22 threadably engaged with the ball bearing screw being moved relativeto the ball bearing screw 24. Accordingly, when the rectilinearly movingcylinder 13 is moved downwardly by the rotation of the injection motor23 and the lid portion 16 of the piston in the back pressure cylinder 12bears against the partition wall 14, the rotary shaft 3 is pushed downand thus, the screw 2 moves forward in the cylinder 1. Also, by therotative driving of the injection motor 23, the ball bearing screw 24 isrotated in the direction opposite to the direction described above tothereby move the rectilineary moving cylinder 13 upwardly, and when thelower end portion of the piston 10 bears against the upper end portionof the shoulder 19 of the rectilinearly moving cylinder, the rotaryshaft 3 is lifted and thus, the screw 2 is retracted upwardly.

The reference numerals 26, 27, 28 and 29 designate sensors for detectingthe stroke of the screw 2. The sensor 26 is a suck back completiondetecting sensor, and the sensor 27 is a volume measuring completiondetecting sensor which detects the vertical position of the screw 2 by asensor dog 9 secured to the middle portion of the rotary shaft 3. Thesensor 28 is a screw overrun detecting sensor, and the sensor 29 is asensor for detecting the waiting position of the rectilinearly movingcylinder 13, and uses the side surface of the rectilinearly movingcylinder 13 as a sensor dog to detect the vertical positions of therectilinearly moving cylinder 13 and the screw 2. The above-describedsensors 26, 27, 28 and 29 are connected to a controller, not shown, andthe signal of each sensor is supplied to the controller 30 to controlthe injection motor 23 and the weight measuring motor 7.

The injection unit base 33 is formed as a unit and has mounted thereonthe injection motor 23, the guide shaft 21, the volume measuring motor7, the heating cylinder 1, etc. However, for the convenience ofillustration, the unit base 33 is shown only fragmentarily.

When actually injection molding is effected, a molding metal mold isdisposed near the fore end of the heating cylinder 1 and also, a deviceor the like for opening and closing the metal mold or clamping the moldis disposed.

Also, it is to be understood that in the present embodiment, a pressurekeeping timer and a cooling timer are provided in the controller 30 tomeasure the pressure keeping time and the cooling time of a moldedarticle in the metal mold cavity.

The operation of the electrically driven type injection apparatus of thepresent embodiment constructed as described above will now be describedwith reference to the operation illustrations of FIGS. 3A-3E and theflow chart of FIG. 4. The symbols indicated with S in parentheses showthe steps in the flow chart of FIG. 4A.

A) The volume measuring and kneading stroke

FIG. 3A shows the state of the measuring and kneading mode. In the caseof the measuring and kneading mode, pressure from back pressuregenerating means 18A acts on the back pressure cylinder 12 in the lowerportion of the rectilinearly moving cylinder through a valve 18 and apressure supply tube 17, and the back pressure cylinder 12 is loadedwith a predetermined pressure.

When the start switch SW₁ of FIG. 4B is closed, the ON signal of therectilinearly moving cylinder waiting position detecting sensor 29, theOFF signal of the measuring sensor 27 and the signal from temperaturedetecting means 1c for measuring the temperature of a heater 1a areinput to a first logic circuit 40A.

A temperature sensor 1b is connected to the temperature detecting means1c, and converts the temperature of the heater 1a into a voltage signal,and in the temperature detecting means 1c, a temperature confirmationsignal is output when the temperature of the temperature sensor 1breaches the temperature of the resin material in its molten state.

The output of the first logic circuit 40A operates a driving circuit 7Afor the volume measuring motor, thereby rotating the volume measuringmotor 7 in a counter-clockwise direction (CCW) shown in FIG. 3A (stepS2).

The screw 2 is rotated through the drive side spur gear 8 and thefollower side spur gear 6 and the material to be molded supplied fromthe hopper 32 is made into a molten state while being kneaded. As thismolten material to be molded is accumulated forwardly of the screw 2 inthe heating cylinder 1, the screw 2 is retracted upwardly in the heatingcylinder 1.

Also, at this time, the back pressure cylinder 12 is in its ON state andtherefore, back pressure is imparted to the screw 2 through the rotaryshaft 3. By such a back pressure operation, bubbles or the like can beprevented from being produced in the molten material to be molded whichis kneaded in the cylinder 1.

If during this measurement and kneading, an electric current foreffecting the servo lock operation of the motor 23 is flowed to brakethe rotation of the ball bearing screw 24 so that the ball nut 22 maynot rotate, an upward thrust as the reaction thereof can act on thepartition wall 14 during the driving of the piston 10 to thereby preventthe rectilinearly moving cylinder 13 from ascending.

Then, as shown in FIG. 3B, the screw 2 ascends and the measuringcompletion detecting sensor 27 becomes ON (step S3). When the sensor 27becomes ON, the supply of electric power from the first logic circuit40A to a driver 7A is cut off and the motor 7 is stopped, thuscompleting the measurement and kneading. The valve 18 which is supplyingpressure to the back pressure cylinder 12 receives the ON signal of themeasuring completion detecting sensor 27 and releases the back pressureaction of the back pressure cylinder (step S5).

B) Suck back stroke

The ON signal of the measuring completion detecting sensor 27 during theaforedescribed measuring and kneading stroke and the OFF signal of thesuck back completion detecting sensor 26 are input to a second logiccircuit 40B. Supply of electric power is effected from the motor drivingcircuit 23A to the motor 23 by the ON signal of the logic circuit 40B torotate the injection motor 23 clockwise.

When the injection motor 23 is rotated clockwise (CW), the rectilinearlymoving cylinder 13 ascends through the ball bearing screw 24 and theball nut 22, and the lower end portion of the piston 10 bears againstthe upper end portion of the shoulder 19 of the rectilinearly movingcylinder and the rotary shaft 3 is lifted, whereby the screw 2 ascends.By this ascension of the screw 2, the pressure in the chamber in thecylinder 1 at the fore end of the screw 2 causes a pressure forcing themolten resin material upward to act so that the molten resin materialbetween the screw and the cylinder may not leak from the injection portat the fore end of the cylinder 1.

This suck back is effected to prevent the molten resin materialvolume-measured at the present step from leaking from the injection portof the cylinder 1 when the metal mold is opened to take out a moldedarticle at the post-step.

When the suck back completion detecting sensor 26 then receives the ONsignal upon this ascension of the screw 2 (step S7), the injection motor23 is stopped (step S8), thus completing suck back.

In FIG. 3C, a indicates the suck back stroke and b indicates themovement stroke of the rectilinearly moving cylinder 13 during suckback.

C) Cooling of the molded article

When at the step S7, the suck back completion detecting sensor 26becomes ON, a cooling time counting counter C₁ for controlling thecooling time of cooling means for cooling the molded article in themetal mold provided below the cylinder 1 terminates counting (step S9).

The cooling of the metal mold at the step S9 is the cooling of the resinpoured into the metal mold cavity during the injection before the stepS1 of the flow chart of FIG. 4A, and the start of the counting by thecooling counter C₁ is effected in the mode of a step S20 which will bedescribed later.

When the cooling of the molded article is completed upon termination ofthe counting by the cooling counter C₁, the clamping of the metal moldis released (step S10), and then the mold is opened (step S11), and themolded article is taken out (step S12), and the mold is again closed(step S13) and is clamped (step S14).

D) Injection stroke

The mold clamp completion signal in the mold clamp mode of the step S14and the signals of the weight measuring sensor 27 and the suck backcompletion detecting sensor 26 are input to a third logic circuit 40C.The injection motor 23 is rotated counterclockwise by the signal of thelogic circuit 40C, whereby the molten resin material is injected intothe metal mold (step S15). That is, by the injection motor 23 beingrotated counter-clockwise (CCW), a downward thrust is imparted to therectilinearly moving cylinder 13. At this time, the rectilinearly movingcylinder 13 is first idly fed, whereafter the thrust transmittingportion 35 of the lower surface of the rectilinearly moving cylinderbears against the spur gear 6 to propel the screw 2.

The control of the motor 23 during the injection is effected by thecontroller 30, and any variation in the value of the consumed electriccurrent of the motor 23 during the completion of the injection isdetected (step S17), and the motor control for injection is changed overfrom speed control (step S16) to current value control (step S18),whereby the injection is completed, and shift is made to a pressurekeeping condition in which a predetermined pressure is applied to thematerial to be molded. That is, control is effected so that the numberof rotations of the motor 23 may become constant in order to keep theinjection speed constant. At this time, as the metal mold cavity isfilled with the material to be molded, the pressure in the molding moldbecomes higher and therefore, it becomes necessary that more electriccurrent flow to the motor 23. Accordingly, in order to determine thisconstant current value, there is provided detecting means 42 fordetecting the electric current flowing to the oil, not shown, of theinjection motor 7, and the output of the detecting means 42 is input tocomparing means 44 for comparison with a predetermined comparativevalue.

E) Pressure keeping stroke

The time when the consumed current value has reached the comparativevalue is the time when the injection stroke is completed. The supply ofelectric power to the motor 23 is kept constant by a constant currentcircuit 46 with the aid of the comparison signal of the comparing means44 to thereby bring about a state in which a predetermined pressure isacting on the resin material in the metal mold cavity. The comparisonsignal from the comparing means 44 causes a pressure keeping counter C₂for controlling the pressure keeping time to start counting (step S18).

Assuming that FIG. 3D shows the time when the injection is completed, cis the rectilinear movement stroke and d is the injection stroke. Thereference numeral 28 designates a screw overrun detecting sensor, and ina normal operation, the injection becomes completed at a position abovethe sensor 28.

When the pressure keeping timer then counts up (step S19), the motor 23is stopped to complete pressure keeping, and by the pressure keepingcompletion signal of the pressure keeping counter C₂, the coolingcounter C₁ starts counting (step S20).

After the completion of the injection, as shown in FIG. 3E, theinjection motor 23 is rotated clockwise (step S21), and therectilinearly moving cylinder 13 is lifted to thereby elevate the screw2. Thereafter, when a signal indicative of ON of the sensor 29 isreceived (step S22), the injection motor 23 is stopped (step S23), andthe rectilinearly moving cylinder 13 waits.

In FIG. 3E, e is the movement stroke of the rectilinearly movingcylinder.

After the steps as described above have been passed, the back pressurecylinder is rendered ON (step S1), and return is again made to the stepshown in FIG. 3A and the volume measuring motor 7 is rotatedcounter-clockwise to start measuring and kneading.

As shown in the above-described embodiment, according to the presentinvention, there can be provided a construction in which the rotaryshaft 3 for rotating the screw 2, the back pressure cylinder 12 forimparting back pressure to the screw and the injection motor 23 forpushing out the back pressure cylinder 12 and imparting an injectionforce to the screw are disposed vertically on the propulsion shaft ofthe screw 2 and therefore, the width and depth in the installation areaare decreased and the apparatus can be easily introduced into theassembly line in which no molding machine could heretofore be installed.

Also, the back pressure during volume measurement can be imparted by theback pressure cylinder 12 provided at a location whereat the rotaryshaft 3 can be directly pressed, and the control of this back pressurecan be accomplished by the pressure control of compressed fluid such asair and therefore, the simplification and compactness of the backpressure device can be realized and the regulation of the back pressurecan be easily accomplished.

Further, the apparatus of the present embodiment adopts a constructionin which the injection motor 23 is directly connected to the ballbearing screw 24 and therefore, there is no necessity of interposing agear or the like therebetween and correspondingly, the cost can bereduced.

In the above-described embodiment, the rotative driving forcetransmitting mechanism is of a construction comprising a combination ofthe wide drive side spur gear 8 and the ordinary follower side spur gear6, but conversely, the follower side spur gear 6 may be made wide andthe drive side spur gear may be made ordinary, and with the rotary shaft3 as a spline shaft, a rotative driving force transmitting mechanism canalso be constructed by a combination of a spline nut engaged with thespline shaft, a timing pulley and a timing belt.

Also, the back pressure mechanism in the above-described embodiment isconstructed of a piston connected to the rotary shaft, a cylinderslidable in the axial direction of the screw and a cylinder slidable inthe axial direction of the screw, but alternatively, the rotation sidemay be constructed into a cylinder and the ball nut side may beconstructed into a piston.

Further, in the above-described embodiment, the rectilinearly movingmechanism is comprised of a ball nut fixed to a cylinder, and a ballbearing screw threadably engaged with the ball nut, but alternatively,the ball bearing screw may be fixed to the cylinder and the ball nut maybe rotatably mounted at a predetermined location on the injection unitbase 33 and may be rotated by the injection motor provided at apredetermined location through a gear or the like.

While the above-described embodiment is constructed as a vertical typemolding machine, the present invention can also be applied to ahorizontal type molding machine.

As described above, the electrically driven type injection apparatus ofthe present invention can be made into a construction in which thescrew, the back pressure cylinder, the rectilinearly moving means andthe second motor are disposed on one and the same shaft, and the entireapparatus can be made slim. Further, it is of course possible to disposethese constituents in a vertical row and thereby narrow the installationspace for the entire apparatus.

Also, in such electrically driven type injection apparatus of thepresent invention, the control of the back pressure to be imparted tothe screw can be directly accomplished by the pressure control ofcompressed fluid such as air supplied to the back pressure cylinder andtherefore, the back pressure imparting means can be constructed by asimple mechanism, and back pressure regulation can be accomplishedsimply.

The injection apparatus of the present invention is designed such thatthe rotational movement and rectilinear movement of the screw areeffected by an electric motor and therefore, of course, the environmentaround the apparatus can always be kept clean.

FIGS. 5 to 8 show a second embodiment of the present invention.

FIG. 5A is a schematic cross-sectional view of the electrically driventype injection apparatus according to the present embodiment, FIG. 5B isa cross-sectional view taken along line II--II in FIG. 5A, FIG. 5C is across-sectional view taken along line III--III in FIG. 5A, FIG. 6 is aperspective view of the vicinity of a rotating mechanism, arectilinearly moving mechanism, a back pressure mechanism, a clutch andan electric motor in FIG. 5, FIGS. 7A-7E illustrate the operation of thepresent embodiment, and FIG. 8 is a flow chart of the injection moldingby the apparatus of the present embodiment.

The electrically driven type injection apparatus of the presentembodiment, as shown in FIGS. 5 and 6, comprises a screw 102 containedin a heating cylinder 101, a spline shaft 103 fixed to the screw 102 bya pin 104, a hollow ball bearing screw guide shaft 105 connected to theupper portion of the spline shaft 103 by a bolt or the like, not shown,and having a stop plate 107 secured to the upper end thereof, a hollowball bearing screw 106 slidably fitted to the ball bearing screw guideshaft 105, and a cylinder rod 133 provided above the guide shaft 105 andbearing against the stop plate 107 of the guide shaft 105 through athrust bearing 135, said constituents being disposed longitudinally onone and the same straight line.

A hopper 129 for supplying a material to be molded into the heatingcylinder 101 is connected to the heating cylinder 101 through a pipe128.

The reference numeral 119 designates an electric motor disposed parallelto these constituents and controlled by a controller 130. The electricmotor 119 is secured to an injection unit base 121 fixedly holding theheating cylinder 101. An input shaft 118 is connected to the electricmotor 119 through a joint sleeve 120. Two upper and lower clutches 116and 117 (the clutch 116 will hereinafter be referred to as the measuringand kneading clutch and the clutch 117 will hereinafter be referred toas the injection clutch) are secured to the input shaft 118. The volumemeasuring and kneading clutch 116 is made connectable to an input timingpulley 114, which is connected through a timing belt 112 to an outputside timing pulley 110 secured to the outer periphery of a spline nut108 fitted to the spline shaft 103. Accordingly, when the clutch 116 isconnected to the pulley 114, the spline shaft 103 is rotated by therotative driving of the electric motor 119 through the pulley 114, thetiming belt 112, the timing pulley 110 and the spline nut 108, wherebythe screw 102 is rotated. The clutch 117 is made connectable to an inputside timing pulley 115, which is connected through a timing belt 113 toan output side timing pulley 111 secured to a ball nut 109. Accordingly,when the clutch 117 is connected to the pulley 115, the ball nut 109 isrotated by the rotative driving of the electric motor 119 through thepulley 115, the timing belt 113 and the timing pulley 111, and alongtherewith, the hollow ball bearing screw 106 moves up and down. Aprojected piece 131 having a cross-section as shown in FIG. 5B isattached to the hollow ball bearing screw 106, and a guide bar 132secured to the injection unit base 121 is fitted to the bifurcated endof the projected piece 131, whereby with the rotation of the ball nut109 the hollow ball bearing screw 106 may not rotate, but may onlyrectilinearly move relative to the guide shaft 105.

The hollow ball bearing screw 106 is slidably fitted to the guide shaft105 as described above and is designed to move up and down with therotation of the ball nut 109, but the stop plate 107 of a largerdiameter than the hollow ball bearing screw 106 is secured to the upperend of the guide shaft 105, and the lower end of the guide shaft 105 issecured to the spline shaft 103 of a larger diameter than the hollowball bearing screw 106 and therefore, when the hollow ball bearing screw106 moves up and down, it bears against the stop plate 107 above andbears against the spline shaft 108 below. Accordingly, since the stopplate 107, the guide shaft 105, the spline shaft 103 and the screw 102are fixed integrally to one another as described above, the hollow ballbearing screw 106 moves up and down to push out the stop plate 107 orthe spline shaft 103 with the rotation of the ball nut 109 operativelyassociated with the rotative driving of the electric motor 119, wherebythe screw 102 can be moved up and down in the heating cylinder 101.

A back pressure cylinder 122 is mounted (not shown) on the injectionunit base 121, and as described above, is disposed on the same straightline as the stop plate 107, the guide shaft 105, the spline shaft 103and the screw 102, and moves the cylinder rod 133 up and down. Therebythe cylinder rod 133 can be lowered to pres the stop plate 107 and applyback pressure to the screw 102. The reference numeral 123 designates apressure regulator for the back pressure cylinder. The pressureregulator 123 is connected to the back pressure cylinder 122 through atube 134, and is also connected to a supply source of compressed fluid(such as air), not shown. The pressing control of the back pressurecylinder 122 is accomplished by effecting the pressure control of thecompressed fluid by the pressure regulator 123.

By the back pressure mechanism of such construction, a thrust can beimparted to the screw 102 against the pressure produced in the moltenmaterial to be molded gradually accumulated forwardly of the screw bythe measuring and kneading of the material to be molded, therebypreventing bubbles or the like from being created in the molten materialto be molded when no back pressure is imparted. Also, the back pressuremechanism of the present embodiment is designed such that as describedabove, back pressure is imparted by the pushing-out operation of theback pressure cylinder 122 and therefore, it is simple in constructionand its control source can be constructed by a simple mechanism, and itsregulation can also be accomplished easily.

A thrust bearing 135 provided at the lower end of the cylinder rod 133and adapted to bear against the stop plate 107 is such that as shown inFIG. 5C, two angular bearings 136 and 137 are symmetrically superposedone upon the other and the inner races of the bearings 136 and 137 arefixed by a nut 138 threadably engaged from the stepped portion of thecylinder rod 133 and the end of the cylinder rod 133 and the outer racesof the bearings are fixed by being nipped by between a cylindricalmember 140 having a shoulder 139 and a cylindrical member 142 having aprotruded portion 141 and when the cylinder rod 133 bears against thestop plate 107, the cylindrical members 140 and 142 rotate and thecylinder rod 133 does not rotate because of the bearings 136 and 137being interposed.

The reference numerals 124, 125, 126 and 127 designate sensors fordetecting the stroke of the screw 102 or the hollow ball bearing screw106. The sensor 124 is a suck back completion detecting sensor, thesensor 125 is a volume measuring completion detecting sensor, the sensor126 is a screw overrun detecting sensor, and the sensor 127 is a hollowball bearing screw waiting position sensor. These sensors 124, 125, 126and 127 are mounted so as to suitably move with respect to the injectionunit base 121 and be capable of adjusting their detecting positions.

Although not shown in FIG. 5A, when injection molding is actuallyeffected, a molding metal mold is disposed on the fore end of theheating cylinder 101 and a device or the like for opening and closing orclamping the metal mold is disposed.

Also, in the present embodiment, it is to be understood that a pressurekeeping timer and a cooling timer are provided in the controller 130 tomeasure the pressure keeping time and the cooling time of the moldedarticle in the metal mold cavity.

The operation of the electrically driven type injection apparatus of thepresent embodiment constructed as described above will now be describedwith reference to the operation illustrations of FIGS. 7A-7E and theflow chart of FIGS. 8A-8B. The symbols shown with S in parenthesesindicate the steps of the flow chart of FIGS. 8A-8B.

In FIG. 7A, the hollow ball bearing screw 106 is in a position forrendering the hollow ball bearing screw waiting position sensor 127 ONand at the same time, the back pressure cylinder 122 and the measuringcluck 116 are also in their ON states (S101). At this time, the motor119 is rotated clockwise (CW) (S102), and the screw 102 is rotated,through the timing belt 112, the spline nut 108 and the spline shaft 103and ascends in the heating cylinder 101 while volume-measuring andkneading the material to be molded supplied into the heating cylinder101. Simultaneously therewith, back pressure is imparted to the screw102 by the back pressure cylinder 122 via the stop plate 107, the guideshaft 105 and the spline shaft 103.

When the screw 102 ascends to the level shown in FIG. 7B, it receives asignal indicative of the volume measuring completion detecting sensor125 being ON (S103). Hereupon, the motor 119 is stopped (S104), and themeasuring and kneading clutch 116 and the back pressure cylinder 122become OFF (S105), thus completing the weight measuring and kneading.

On the other hand, when as described above, the measuring and kneadingof the material to be molded are being affected in the cylinder 101, thematerial to be molded measured and kneaded at the previous step iscontained in the metal mold (not shown) provided below the cylinder 101,whereupon pressure keeping, cooling and taking-out of the molded articleare effected. At this time, it is necessary to effect suck back toprevent the material to be molded kneaded in the cylinder 101 fromleaking from the injection port of the cylinder 101.

So, the measuring and kneading in the cylinder 101 are completed asdescribed above the motor 119 becomes OFF (S104), and the measuring andkneading clutch and the back pressure cylinder are rendered OFF. Here,when the injection clutch 117 is rendered ON (S106), the motor 119 isrotated clockwise (CW)(S107). When the hollow ball bearing screw 106ascends thereby through the timing belt 113 and the ball nut 109, thestop plate 107 is thrust up and suck back is effected. This suck back iseffected until the hollow ball bearing screw 106 ascends to a positionshown in FIG. 7C for rendering the suck back completion detecting sensor124 ON (S108). At this time, the motor 119 is stopped (S109) and thesuck back is completed. In FIG. 7C, a is the suck back stroke and b isthe hollow ball bearing screw movement stroke during the suck back.

When the suck back is completed as described above and thereafter, thecooling timer counts up (S110), the clamping of the metal mold isreleased (S111) and the mold is opened (S112) and the molded article istaken out (S113), whereafter the mold is again closed (S114) and themold is clamped (S115).

Subsequently, the motor 119 is rotated counter-clockwise (CCW) (S116) toinject the kneaded material to be molded into the metal mold clamped asdescribed above. At this time, the injection clutch 117 is continuedlyin its ON state and therefore, when the motor 119 is rotatedcounter-clockwise, a downward thrust is imparted to the hollow ballbearing screw 106. At this time, the hollow ball bearing screw 106 isfirst idly fed, whereafter as shown in FIG. 7D, the lower end portion ofthe hollow ball bearing screw 106 strikes against the shoulder 103a ofthe spline shaft and the screw 102 is pushed downwardly, whereby theinjection into the metal mold takes place. Since the back pressurecylinder 122 is OFF, the cylinder rod 133 remains in the position ofFIG. 7C.

The control of the motor 119 during injection is effected by thecontroller 130, any variation in the consumed current value of the motor119 at the completion of injection is detected (S118), and the controlof the motor for injection is changed over from the speed control (S117)to the current value control (S119), whereby injection is completed, andshift is made to a pressure keeping state in which a predeterminedpressure is applied to the material to be molded. That is, the number ofrotations of the motor 119 is made constant to make the descending speedof the ball bearing screw 106 constant, and injection is effected at aconstant speed. However, during this injection, the pressure of thematerial to be molded becomes higher as the metal mold cavity is filledwith the material to be molded and therefore, to maintain a constantinjection speed as described above, it is necessary that a graduallyincreasing electric current flow to the motor 119. Accordingly, bydetermining a constant current value and regarding the time when theconsumed current value has reached this constant value as the time ofcompletion of injection, the time of completion of injection can bedetected by the measurement of the consumed current value. By changingover the control to such control that at this time of completion ofinjection, the value of the electric current imparted to the motor 119becomes constant, a constant pressure can be applied to the material tobe molded in the metal mold cavity to thereby accomplish pressurekeeping.

After the motor 119 has been changed over to the current value control,the counting by the pressure keeping timer is started (S119). Assumingthat FIG. 7D is the state in which injection has been completed, c isthe hollow ball bearing screw movement stroke and d is the injectionstroke. The reference numeral 126 designates a screw overrun detectingsensor, and in the normal operation, injection becomes completed at aposition above the sensor 126.

When the pressure keeping timer then counts up (S120), the motor 119 isstopped to complete pressure keeping, and the counting by the coolingtimer is started (S121).

When pressure keeping is completed as described above, the motor 119 isrotated clockwise with the injection clutch 117 kept in its ON state toprepare for the next measuring and kneading (S122), and the hollow ballbearing screw 106 is lifted until the hollow ball bearing screw waitingposition sensor 127 becomes ON, and when the hollow ball bearing screwwaiting position sensor 127 is rendered ON (S123), the motor 119 isstopped (S124) and the hollow ball bearing screw 106 is caused to waitat that position as shown in FIG. 7E. At this time, the injection clutch117 is rendered OFF (S125). In FIG. 7E, e is the hollow ball bearingscrew movement stroke.

After the steps as described above have been passed, the volumemeasuring clutch 116 and the back pressure cylinder are again renderedON (S101), and the above-described steps are repeated, whereby thekneading and measuring of the material to be molded, back pressure, suckback and injection can be effected.

As described above, in the present embodiment, the screw rotating splineshaft, the screw propelling hollow ball bearing screw, etc. are disposedvertically on the same straight line on the propulsion shaft of thescrew so that the back pressure control during measuring may be effectedby the pressure control of compressed fluid such as air supplied to thecylinder provided at the rear end of the guide shaft 105 and therefore,the simplification of the back pressure device and the facilitation ofregulation become possible. At the same time, the compactness of thescrew propelling and rotating mechanism becomes possible.

Especially in the present embodiment, the injection apparatus is of thevertical type and therefore, the width and depth in the installationarea are reduced and thus, it has become possible that the apparatus iseasily introduced into an assembly line in which no molding machinecould heretofore be installed.

Further, in the present embodiment, a series of operations of the screwsuch as measuring, kneading, suck back and injection are effected by asingle electric motor 119 and two clutches 116 and 117 and therefore, amore inexpensive injection apparatus has become possible.

In the above-described embodiment, the spline shaft 103 is provided atthe rear end of the screw 102 and the hollow ball bearing screw guideshaft 105 is provided at the rear end thereof, but alternatively, thehollow ball bearing screw guide shaft may be provided at the rear end ofthe screw and the spline shaft may be provided at the rear end thereofto thereby provide a rectilinearly moving mechanism and a rotatingmechanism in the named order. In this case, the back pressure cylinderis provided so as to press the rear end of the spline shaft.

In the above-described embodiment, the guide shaft 105 is made smallerin diameter than the spline shaft 103 and the boundary portion betweenthe guide shaft 105 and the spline shaft 103 is provided as arestraining portion below the hollow ball bearing screw 106, but wherethe guide shaft 105 is larger in diameter than the spline shaft 108, aflange portion or the like having a diameter larger than the diameter ofthe hollow ball bearing screw is provided in said boundary portion,whereby the restraining portion of the hollow ball bearing screw isformed.

Also, in the above-described embodiment, the rotary shaft of therotating mechanism is employed as the spline shaft and the rotativedriving force transmitting mechanism is comprised of the timing pulley114, the timing belt 112, the timing pulley 110 and the spline nut 108,but alternatively, there may be adopted a construction in which therotary shaft is replaced by a wide gear and a gear meshing with theinput shaft 118 is mounted on the input shaft and the gear mounted onthe input shaft 118 slidably transmits a rotational force to the widegear.

Also in the rectilinearly moving mechanism, instead of using the timingbelt 113, a gear may be mounted on the ball nut 109 and a gear meshingwith the input shaft 118 may also be mounted on the input shaft, andthis may be employed as the rotative driving force transmittingmechanism in the rectilinearly moving mechanism.

Further, the above-described embodiment is designed such that therotating mechanism and the rectilinearly moving mechanism are driven bya single motor 119 and two clutches 116 and 117, but alternatively, theclutches may be eliminated and an electric motor may be used for each ofthe rotating mechanism and the rectilinearly moving mechanism.

Furthermore, the above-described embodiment is a vertical type moldingmachine, but the present invention can also be easily applied to ahorizontal type molding machine.

As described above, in the electrically driven type injection apparatusof the present invention, a screw contained in a cylinder, a rotatingmechanism for rotating the screw, a forwardly moving mechanism formoving the screw forwardly and a back pressure mechanism for impartingback pressure to the screw are successively arranged on the propulsionshaft of the screw. Therefore, the compactness of the mechanisms forforwardly moving and rotating the screw becomes possible and forexample, by disposing the respective elements vertically, theinstallation area for the apparatus may be very small.

Also, the injection apparatus of the present invention is of aconstruction in which the rotational movement and forward movement ofthe screw are accomplished by electric motors and therefore, theenvironment around the apparatus can always be kept clean.

Further, if there is adopted a construction in which the rotationalmovement and forward movement of the screw are accomplished by a singleelectric motor provided with a clutch mechanism, the cost required ofthe injection apparatus may be low.

Also, in the present invention, the back pressure mechanism of the screwcan be effected by the pushing-out operation of the back pressurecylinder and therefore, the construction becomes simpler and the controlsource therefor can be constructed by a simple mechanism, and regulationcan be accomplished easily.

What is claimed is:
 1. An electrically driven injection moldingapparatus, comprising:a screw for kneading a material to be molded in acylinder; a first motor for rotating said screw and measuring an amountof said material to be molded; a back pressure cylinder connected tosaid screw for imparting back pressure to said screw; rectilinearlymoving means connected to said back pressure cylinder for rectilinearlymoving said back pressure cylinder; a second motor for driving saidrectilinearly moving means; a volume measuring sensor for detecting thecompletion of measuring and outputting a signal; a sensor dog connectedto said crew; and first logic means for receiving the signal from saidvolume measuring sensor as an input sensor and controlling said firstmotor.
 2. An apparatus according to claim 1, further comprising:asuction pressure detecting sensor; and second logic means for receivingsignals emitted from said suction pressure detecting sensor and saidvolume measuring sensor as inputs and drivingly controlling said secondmotor.
 3. An apparatus according to claim 1, further comprising a ballnut receiving member fixed to a rotary shaft to which said screw isconnected, an injection motor serving as said second motor, a ballbearing screw connected to an output shaft of said injection motor andthreadably engaged with a ball nut secured to said ball nut receivingmember, and a volume measuring motor serving as said first motor isconnected to said rotary shaft through a rotation transmitting gear,wherein said volume measuring motor is braked during the rotativedriving of said injection motor to thereby stop the rotation of saidball nut.
 4. An apparatus according to claim 3, further comprising:aninjection completion detecting sensor; and change-over means for saidinjection motor, said change-over means changing over said injectionmotor from speed control to an electrical current value control.
 5. Anapparatus according to claim 4, wherein said change-over meansincludes:comparing means for detecting an electric current of saidinjection motor and detecting whether the electrical current value hasreached a predetermined value; and constant current means for supplyinga constant current to said injection motor based on a signal from saidcomparing means.
 6. An apparatus according to claim 5, furthercomprising a pressure keeping counter adapted to start counting by thesignal of said comparing means.